Common Demulsifiers – The non-ionic demulsifiers commonly used in oilfields today mainly include the following types:

1. SP-type demulsifiers are primarily composed of polyoxyethylene polyoxypropylene octadecyl ether, with the theoretical structural formula R(PO)x(EO)y(PO)zH. In this formula, EO represents polyoxyethylene, PO represents polyoxypropylene, R represents fatty alcohols, and x, y, z represent the degree of polymerization. SP-type demulsifiers appear as a pale yellow paste, with an HLB value of 10 to 12, and are soluble in water. These non-ionic demulsifiers are particularly effective in breaking down paraffin-based crude oils. The hydrophobic portion of the molecule is made up of carbon chains with 12 to 18 carbon atoms, while the hydrophilic groups form hydrogen bonds with water through the hydroxyl (-OH) and ether (-O-) groups in the molecule. However, due to the relatively weak hydrophilicity of these groups, it is not possible to pull the hydrophobic carbon chains into water with just one or two hydroxyl or ether groups; multiple such hydrophilic groups are required to achieve solubility in water. The larger the molecular weight of the non-ionic demulsifier and the longer its molecular chain, the more hydroxyl and ether groups it contains, and the stronger its ability to break down the emulsion of crude oil. Another reason why SP-type demulsifiers are suitable for paraffin-based crude oils is that such crude oils contain little or no gum and asphaltenes, resulting in fewer lipophilic surfactants and a lower relative density. For crude oils with higher levels of gum and asphaltenes (or with a water content of more than 20%), the demulsifying ability of SP-type demulsifiers is weaker due to their simple molecular structure, which lacks branched and aromatic structures.

2. AP-type demulsifiers are polyoxyethylene polyoxypropylene polyethers initiated by polyethylene polyamine, and they are branched non-ionic surfactants with the molecular formula D(PO)x(EO)y(PO)zH. In this formula, EO represents polyoxyethylene, PO represents polyoxypropylene, R represents fatty alcohols, and D represents polyethylene polyamine; x, y, z represent the degree of polymerization. AP-type demulsifiers are more effective in breaking down paraffin-based crude oil emulsions than SP-type demulsifiers, and they are particularly suitable for crude oils with a water content of more than 20%. They can also achieve rapid demulsification at low temperatures. For example, while SP-type demulsifiers require 2 hours at 55 to 60°C to achieve demulsification, AP-type demulsifiers only need 1.5 hours at 45 to 50°C. This is due to the structural characteristics of the AP-type demulsifier molecules. The use of polyethylene polyamine as an initiator results in molecules with longer chains and more branches, giving them higher hydrophilic properties than the simpler SP-type demulsifiers. The branched structure of AP-type demulsifiers also provides them with better wetting and penetration properties. When breaking down crude oil emulsions, the molecules of AP-type demulsifiers can quickly penetrate the oil-water interface membrane, occupying more surface area than the straight-chain monolayer of SP-type demulsifier molecules. As a result, less of this demulsifier is needed, and the demulsification effect is more pronounced. Currently, this type of demulsifier is widely used in the Daqing oilfield.

3. AE-type demulsifiers are also polyoxyethylene polyoxypropylene polyethers initiated by polyethylene polyamine, but they are two-stage polymers with smaller molecules and shorter branches. The molecular formula for AE-type demulsifiers is D(PO)x(EO)yH, where EO represents polyoxyethylene, PO represents polyoxypropylene, D represents polyethylene polyamine, and x, y represent the degree of polymerization. Although there are significant differences in the molecular structure of AE-type and AP-type demulsifiers, their molecular components are the same; the differences lie in the amount of monomer used and the order of polymerization. 

   (1) During the design and synthesis of these two types of non-ionic demulsifiers, the amounts of materials used at the head and tail of the molecules are different, resulting in varying lengths of the polymerized molecules.

   (2) The molecules of AP-type demulsifiers are two-stage polymers initiated by polyethylene polyamine, and they form block copolymers with polyoxyethylene and polyoxypropylene. The molecules of AE-type demulsifiers are also two-stage polymers initiated by polyethylene polyamine, but they form two-stage copolymers with polyoxyethylene and polyoxypropylene. Therefore, the molecules of AP-type demulsifiers designed in this way are expected to be longer than those of AE-type demulsifiers. AE-type demulsifiers have a two-stage, branched structure and are also suitable for breaking down asphaltenic crude oil emulsions. The higher the content of lipophilic surfactants in asphaltenic crude oils, the stronger the viscosity and the smaller the density difference between oil and water, making it more difficult to demulsify the oil. However, AE-type demulsifiers can achieve rapid demulsification. Additionally, AE-type demulsifiers are also effective as wax inhibitors and viscosity reducers. Due to their branched molecular structure, they can easily form tiny networks that cause the paraffin crystals already present in the crude oil to fall into these networks, preventing the crystals from connecting with each other and forming a networked structure of paraffin. This reduces the viscosity and freezing point of the crude oil, prevents the aggregation of wax crystals, and thus achieves the purpose of wax inhibition.

4. AR-type demulsifiers are new types of water-soluble non-ionic demulsifiers made by combining alkylphenol formaldehyde resin (AR resin) with polyoxyethylene and polyoxypropylene. They have an HLB value of around 4 to 8 and can achieve demulsification at temperatures as low as 35 to 45°C. The molecular formula for AR-type demulsifiers is AR(PO)x(EO)yH, where EO represents polyoxyethylene, PO represents polyoxypropylene, AR represents the resin, and x, y, z represent the degree of polymerization. During the synthesis of these demulsifiers, AR resin acts both as an initiator and as a component of the demulsifier molecule, forming lipophilic groups. The characteristics of AR-type demulsifiers include their small molecular size, which allows them to dissolve, diffuse, and penetrate well even when the freezing point of the crude oil is above 5°C. This enables them to cause the emulsified water droplets to flocculate and coalesce. They can remove more than 80% of the water from crude oils with a water content of 50% to 70% within 45 minutes at temperatures below 45°C, which is beyond the capabilities of SP-type and AP-type demulsifiers.